GB2142302A - Breakaway bail - Google Patents

Description

1

SPECIFICATION

Breakaway bail This invention relates to pedestal mount 70 cranes, and more particularly, to bails for use with such crane.

The present invention provides a bail for a crane, especially for pedestal mount cranes intended for use on offshore platforms, which permits a predetermined and preferred mode of failure. When a crane situated on an off shore platform is working with a ship, acci dentally entangling the crane's hook with components attached to, or carried by the ship is possible, especially in rough seas. The severe overload conditions created upon such an occurrence, may rip the crane from its pedestal mounting causing the entire crane.

and any personnel thereon, including the op erator, to fall into the sea. The present inven tion prevents such a result by predetermining the mode of failure and insuring such failure is in a manner to minimize both the hazard to personnel and the damage to the crane and adjacent property.

The drawings are briefly described as foi l ws:

Figure 1 is a side elevational view of the crane incorporating the present invention; Figure 2 is a detailed view, in side elevation of the preferred embodiment of the bail ac cording to the present invention; and Figure 3 is a top plan view of the bail shown in Fig. 2.

Referring to Fig. 1, a crane, indicated generally at 10, is swingably mounted on a pedestal 12 which is rigidly attached to an offshore platform, for example. The swinging movement is provided by a turntable 14 con- 105 nected to the pedestal 12 and to the frame 16 of the crane. A boom 18 is pivotally mounted on the frame 16 and is angularly adjustable by a boom hoist 20 mounted on a winch frame 22. The winch frame 22 also supports an auxiliary hoist 24 and a main hoist 26. A whip line 28, having a hook 30 attached to its free end, is trained over sheaves 32 and 34 rotatably mounted on a boom tip extension 36 and wound on the auxiliary hoist 24. Main hook block 38 is suspended by a wire rope 40 trained over a sheave or sheaves (not shown) on the boom tip and wound on hoist 26.

A winch frame 22 is attached at its forward end to the frame 16 of the crane and is supported by a pair of links, one of which is shown at 42, pinned by pins 25 to the frame 16 and by pins 46 to the rearward end of the winch frame 22. An A-frame gantry, indicated generally at 23, comprises a pair of vertical legs 48 and a pair of angled or slanted legs 50. Each of the legs 50 is pinned at its lower end by a pin 52 to a bracket secured to the winch frame 22. Each of the vertical legs 48 GB 2 142 302A 1 is pinned to the winch frame 22 by pin 54 positioned vertically above the corresponding pin 46 and by pin 56 to a bracket attached to the upper end of each leg 50. A cross-brace (not shown) extends between and is secured to the legs 50. A bail, indicated generally at 60, is pinned to, and positioned between the brackets on the legs 50 by a pin 58. A wire rope 62 wound on boom hoist 20 is reeved between a multiple sheave bridle 64, which is secured to the tip of the boom 18 by pendants 66, and the sheaves carried by the bail 60; the rope 62 being secured to or deadended at the bail 60. Reeling in the wire rope 62 by the boom hoist 20 causes the boom tip to be elevated, i.e. the boom radius reduced, and unwinding the wire rope 62 causes the boom tip to be lowered, i.e. the boom radius increased.

Referring now to Figs. 2 and 3, the bail 60 has a pair of parallel tension plates 72 and 74 secured to the ends of a tube 68. A pair of ring members 76 and 78, each having a bushing secured within a central bore, are secured to the outer surfaces of the plates 72 and 74 respectively and are positioned generally in line with the center of the tube 68. The interior diameter of the tube 68 is larger than the interior diameter of the bushings 70 so that the pin 58 engages only the bushings 70. The tube 68, plates 72 and 74 and ring members 76 and 78 are positioned between, and pivotally secured to the brackets on the upper ends of the legs 50 by the pin 58; the pin 58 thereby defining a pivot axis for the bail 60.

Each of the plate members 72 and 74 has a circular section 80 attached to the tube 68 and the adjacent ring 76 or 78 which makes a smooth transition to an arcuate neckeddown section 82. A triangular section 84 is formed on the end of each plate 72 and 74 opposite the circular section 80. A transverse beam 86 having an upright flange 88 is secured between the plates 72 and 74. A multiple sheave pulley 87 is rigidly secured to the beam 86 by means of brackets 90. The beam 86 transfers the loads imposed on the pulley 87 to the plates 72 and 74. Since the bail 60 can pivot and since the forces applied to the pulley are through a wire rope, the plates 72 and 74 are subjected to stresses which are nearly pure tension. The neckeddown section 72 is designed so that the stress in its minimum cross-sectional area 92 will reach the yield point before any other component of the crane. Thus, the bail 60, specifically the tension plates 72 and 74, will fail by separation across the necked-down section.

The safety factor designed into the neckeddown section 82 is adequate to withstand those loads anticipated and actually encountered during normal operation of the crane. However, when the loads become excessive, as when the hook accidently becomes entan- 2 GB 2 142 302A 2 gled with a ship, the resulting stresses in the necked-down section will be of a magnitude to cause separation thereacross. With such separation, the loading on the crane is reduced. Of course, without the bail 60 to support the boom it will start to fall. As it fails, the hook 30 and hook block 38 will move toward the boom tip because of the associated reeving and the difference in the pivot axis for the boom and the associated winch. Depending upon the position of these two hooks relative to the boom and the angle of the boom, one of the hooks may engage the boom, in what is commonly called a two- block condition, which would then tend to slow or retard the fall of the boom. In any event, the crane will remain on its pedestal, and only relatively minor repair or replacement of damaged crane components will be required to return the crane to service.

Claims (4)

1. CLAIMS 1. A breakaway bail for a crane having a hook comprising: 25 a

   tension plate means; bushing means attached to said plate means for pivotally mounting said bail; and said tension plate means having a section of reduced cross-sectional area so that under excessive load said plate means will separate.
2. 2. In a crane having a boom supporting a hook and a gantry to support the boom, a breakaway bail comprising:

   tension plate means; bushing means attached to said plate means for pivotally attaching said tension plate means to said gantry; reeving means for operative connection of said boom to said plate means; and said tension plate means having a section of reduced cross-sectional area so that under excessive load said plate means will separate.
3. 3. A breakaway bail for use with a crane having a boom for suspending a hook and a gantry operatively connected to said boom through said bail, said bail comprising:

   a pair of parallel tension plates; a spacer tube secured between said plates; a pair of rings, each having a bushing, secured to the outside of said plates in substantial alignment with said tube; pin means engageable with said bushings for pivotal attachment to said gantry; a beam secured between and to said plates; a multiple sheave pulley affixed to said beam; said plates having a necked-down section between said tube and said beam; said section being stressed to yield when an excessive load is applied to said hook.
4. 4. A breakaway bail according to claim 1 and substantially as described with reference to or as shown by the Drawings.

   Printed in the United Kingdom for Her Majesty's Stationery Office. Dd 8818935, 1985. 4235 Published at The Patent Office, 25 Southampton Buildings. London. WC2A lAY, from which copies may be obtained